diff options
Diffstat (limited to 'doc/dbus-specification.xml')
| -rw-r--r-- | doc/dbus-specification.xml | 24 |
1 files changed, 21 insertions, 3 deletions
diff --git a/doc/dbus-specification.xml b/doc/dbus-specification.xml index 3e8f8ec9..208a8e91 100644 --- a/doc/dbus-specification.xml +++ b/doc/dbus-specification.xml @@ -3386,7 +3386,8 @@ <para> Messages may have a <literal>DESTINATION</literal> field (see <xref - linkend="message-protocol-header-fields"/>). If the + linkend="message-protocol-header-fields"/>), resulting in a + <firstterm>unicast message</firstterm>. If the <literal>DESTINATION</literal> field is present, it specifies a message recipient by name. Method calls and replies normally specify this field. The message bus must send messages (of any type) with the @@ -3396,9 +3397,26 @@ </para> <para> - Signals normally do not specify a destination; they are sent to all + When the message bus receives a signal, if the + <literal>DESTINATION</literal> field is absent, it is considered to + be a <firstterm>broadcast signal</firstterm>, and is sent to all applications with <firstterm>message matching rules</firstterm> that - match the message. + match the message. Most signal messages are broadcasts. + </para> + + <para> + Unicast signal messages (those with a <literal>DESTINATION</literal> + field) are not commonly used, but they are treated like any unicast + message: they are delivered to the specified receipient, + regardless of its match rules. One use for unicast signals is to + avoid a race condition in which a signal is emitted before the intended + recipient can call <xref linkend="bus-messages-add-match"/> to + receive that signal: if the signal is sent directly to that recipient + using a unicast message, it does not need to add a match rule at all, + and there is no race condition. Another use for unicast signals, + on message buses whose security policy prevents eavesdropping, is to + send sensitive information which should only be visible to one + recipient. </para> <para> |